does multiple shard key helps performance in mongodb?

Since sharding databas开发者_Go百科e use shard key to split chunk AND route queries, so I think maybe more shard key can helps to make more queries targeted

I tried to specify multiple keys like this

db.runCommand( { shardcollection : "test.users" , key : {_id:1, email : 1 ,address:1}

but I have no idea if it works and what the downsides of doing this

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To be clear here, you can only have one shard key. So you cannot have multiple shard keys.

However, you are suggesting a compound index as the shard key. This can be done, but there are some limitations.

For example the combination of _id, email and address must be unique.

Documents for choosing a shard key. There are several more considerations that I cannot list here. Please see that document.

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Selection of shard key based on :

{coarseLocality : 1, search : 1}

coarseLocality is whatever locality you want for your data, search is a common search on your data.

You must have an index on the key you shard by, so if you choose a randomly-valued key that you don’t query by, you’re basically wasting an index. Every additional index makes writes slower, so it’s important to keep the number of indexes as low as possible.

So,increasing shard key combination doesn't help much.

Extract taken from Kristina Chodrow's book "Scaling MongoDB".